This application relates to a shot tube for injecting molten metal into a die-cast mold.
Die casting is a metal casting technique that employs the use of permanent, reusable molds in which molten alloys are injected and compressed into the cavities to form the desired component. The die cast system is comprised of multiple components: the molds, the shot tube, the shot rod and piston, the frame of the machine, a hydraulic system, pneumatic system, and a programmable logic controller to control the interconnected systems.
Die-cast molds are known and utilized to form any number of components. A die-cast machine is comprised of a fixed platen and a moving platen. In a split die set one half of the mold mounts the stationary platen and the second half to the moveable platen. The moving platen is actuated by hydraulic piston, and mechanical clamping system to position the moveable die half in the appropriate position during each phase of the die casting process. A singular or array of cavities are formed between the two die halves in the shape of a component which is to be cast.
The desired alloy is liquefied by a variety of methods and is transferred to or directly poured through the opening in a shot tube. The molten alloy is added to the desired fill level for the component, the hydraulic injection system is activated, and the piston pushes the molten metal along the shot tube delivering the molten material into the cavity. As the molten metal begins to solidify, an intensification cycle can be used to further compress the semisolid alloy into the die cavity to minimize casting defects such as shrinkage and non-fill of the cavities. Upon solidification the component is formed into the shape of the cavity.
Historically, the shot tubes have been mounted to the fixed platen in traditional machines that operate in air. While this is suitable for low temperature alloy system, the stack up of tolerances that causes misalignment and gaps is extremely problematic for quick solidifying high temperature alloys. The desire to improve the quality of existing alloys and the opportunity to cast higher temperature capable alloys such as: steels, iron-nickel super alloys, nickel super alloys, and cobalt super alloys creates the need to operate the die casting system in a vacuum to ensure metallurgical quality and elimination of defects such as dross and ceramic inclusions from these alloy systems.
Conventional mounting of the shot tube poses significant challenges as a result of need to operate the system in a vacuum. Mounting the tube in the traditional manner would require extensive sealing between the tube and the platen to prevent the flow of an oxidizing atmosphere into the tube. In order to minimize vacuum leaks and maintenance of the tube an alternative method of mounting and aligning the tube is required to ensure optimal operation and serviceability of the equipment.
In one particular die-cast system, an electron beam device is utilized to melt an ingot of metal within a vacuum chamber. The molten metal drips into a water cooled copper crucible as the ingot is superheated by the electron beam. When a sufficient amount of material has filled the crucible, the electron beam sweeps across the surface until the system has achieved the desired temperature, the dross is swept to the rear of the crucible, the system is tilted and the molten metal is poured through the opening in the shot tube. In this embodiment, the fixed platen does not easily mount the shot tube.